PPF/PAR

[LowWater]

Photosynthetic Photon Flux (micromol/m^2/sec) under the Photosynthetically Active Radiation curve (PPF per PAR) is a conceptual way of evaluating LED grows that I'm hearing more and more frequently. There are two aspects I fail to understand. 1) Every strain of every species of plant has its unique PAR. 2) A given strain's PAR changes in time from germination through harvest.

If I'm correct above, how could one ever design a superior LED grow light once you've realized the potential of its components?

Is this why we rarely see A:B comparisons of 2 LED grows of 1 clone, or reviews in general?

 

[Seamaiden]

Are you certain that each strain has its own PAR preference? My thinking is like this--everything evolved under the same sun. The main changes in radiation we might see are more with strength/intensity of light (think tropical vs extreme latitudes, shade vs full sun, PPF/PPFD), and while there must (may? I'm not actually sure about that) be some slight shift in wavelengths, I don't think we have to do much more or other than ensuring the plant receives sufficient PUR (photosynthetically usable radiation, which is a different metric than PPF, or PAR).

Now, when you discuss the various light 'needs' of a flowering plant through its life, I believe that the issue is twofold--photoperiodisim, and phytochrome switching, which in flowering plants like Arabidopsis are attuned to red wavelengths, IF I understand what I've read correctly.

Mmm.. chewing on your question a little more, here's the meat of what I think you're trying to ascertain: DO different strains have different wavelength requirements (PAR)? The answer in my experience is no, they don't. You also seem to be asking if there is a spectrum shift required, and the answer for cannabis is sort of. You can flower under lights that are pushing (peaking) less in the red areas that trigger hormonal response (that is responsible for stuff like what phase of growth the plant is in, vegetative or regenerative, aka flowering), but you will see diminished yield and quality than if using a spectrum that has peaks in the proper areas of the spectrum, giving sufficient 'push' (PPF, or PPFD).

Does that make sense? I am nothing resembling an expert on this, but I did grow many giant clams under homemade light hoods way back when. :D And, I've stayed at a Holiday Inn, but not recently. I prefer Crowne Plaza, to be perfectly honest, and Marriot is all buck and no bang.

 

[LowWater]

Seamaiden, thank you for your gentle and swift reply. I anticipated getting hammered. And you're right about Marriot. Here's an unsolicited opinion. Go to the best high-brow casino in your destination, sit down at a poker table in the card room, preferably a game you understand, and ask the dealer if you may speak with the floor manager. Let him/her know that you plan to play most of the evening and could they arrange a room. This I know. LEDs not so much. I look at natural flora as it shifts up and down various latitudes, and hear about strains of cannabis that are notoriously difficult to grow indoors, or quite easy to grow indoors. I'm willing to yield on the lifecycle argument as evolution would have knocked off those seedlings with picky, unfulfillable outdoor requirements, but if you are correct about different strains having similar PPF/PAR needs, what is so difficult in deciphering it? Grant me this: it seems to be a terrific sticking point. Why can't engineers adjust their diode map until they've filled the area under the PAR curve?

There is something I am not understanding in this two-fold question and I'm not sure what it is. I'm a scientist but neither a botanist nor physicist.

Take Care.

 

[Seamaiden]

You're quite welcome! I'm not a gambler, but a friend has suggested a trip to Las Vegas for the food and the shows, and my husband and I were married in the now-razed Stardust Hotel, in a very touching ceremony.

In any event, I'm not really up to date on the current state of the technology of LEDs, but when I first read of some reefkeepers burning high-intensity-requiring anemones with their... Cree lights I think was what they used (made their own rig, IIRC), I knew that LEDs had huge potential. The issue for growing terrestrial plants wouldn't be what I call 'push' (PPF/PPFD), but spectrum (wavelength). I know that because when growing photosynthetic organisms like corals and anemones and giant clams under water we don't only have the inverse square law to deal with, we're also trying to 'push' light through water, and the deeper you go the MUCH more difficult it becomes. Because of my background in this area, I understand what's happening fairly well, well enough to mix my own shop lights and grow all but the most high-light-requiring organisms under them. Obviously, the closer to equatorial tropical sun you can get, the better, and that's a LOTTA push. Because of the water and the technology, LEDs became strong and well represented in the wavelengths required for growing aquatic photosynthetics, which are primarily in the blue end of the spectrum, very little to no red (this is why many deepwater animals are red or deep orange--they disappear at depth because the red wavelength is filtered out by the water, and thus, why water sans microbes is blue).

Still with me?

So! The LED engineers/manufacturers, in order to meet the horticultural market, had to develop diodes that emit the right spectrum, and it seems with LEDs that this is becoming easier/more common, and they're also becoming very precise. It's much more complicated stuff because we're dealing with the full spectrum of the sun and what the plants actually use, along with the limits of what the plant can use (that's where the photon flux density shit comes in).

Has that helped you conceptualize it, or am I headed off in the wrong direction for what you're trying to get answered? I'm hoping that someone who's more well versed in this technology chimes in.

 

[LowWater]

Did you ever see the Seinfeld episode where George claimed to be a Marine Biologist

all to impress a woman? I can't imagine you missed it unless you're one of those brilliant 20 year-olds who chooses not to watch television.

I'm sort of with you so far, but am getting a bit lost applying Snell's law to refraction and spectral penetration. When white light from a vacuum impacts on any non-vacuum surface (like an atmosphere) at any incident angle other than 0, the refracted angle is more acute to the perpendicular inversely proportional to its wavelength. I hope my language isn't falling apart here. Anyway, the super-hip, super fast (UV) wavelengths penetrate much more efficiently that the sluggish (IR) wavelengths which sort of smear up toward the parallel. Same with "pushing" through water.

I always assumed that this was why LEDs were more effective with the vegetative phase of the plant's growth wherein the bimodal PAR is more dependent on the blues. Hence the use of Metal Halides in HID vegitative setups, then just blasting the dickens out of your canopy with an inefficient fusillade of orange/reds courtesy of the HPS lights for flowering).

But this seems easy to address in LEDs if I'm right and, of course, irrelevant if I'm wrong.

Am I wrong?

P.S. I found an Interactive Java Tutorial at:
http://micro.magnet.fsu.edu/optics/lightandcolor/refraction.html
It's 1st on the page and entitled, "Refraction of Light". It explains my second paragraph much better than I did.

 

[Seamaiden]

I don't think you're wrong, I think you've got the idea (me, too, I think. I hope!).

It's been more years than I can recall since I've watched something like a sitcom, I'm sorry, I don't recall that episode!